1. Field of the Invention
This invention relates to a method of generating a complex curved surface comprising at least two three-dimensional curved surfaces, and more particularly, to a complex curved surface creation method for generating a complex curved surface in which a predetermined roundness is provided at a portion where first and second three-dimensional curved surfaces intersect.
2. Description of the Related Art
A curved surface of a three-dimensional metal mold or the like on a design drawing is generally expressed by a plurality of section curves, but no profile data is shown for the shape of the area lying between a certain section curve and the next adjacent section curve. In numerically controlled machining it is essential that machining be carried out so as to smoothly connect these two section curves despite the fact that the profile between them is not given. In other words, this means that machining must be performed by generating the curved surface between the two section curves from such data as that indicative of the section curves, recording on an NC tape the data concerning the generated curved surface, and carrying out machining in accordance with commands from the NC tape. To this end, there has been developed and put into practical use a method comprising generating a plurality of intermediate sections in accordance with predetermined rules using data specifying several sections and section curves of a three-dimensional curved body, finding a section curve (intermediate section curve) on the curved body based on the intermediate sections, and generating a curved surface of the three-dimensional body based on the plurality of generated intermediate section curves. For example, see the specification of Japanese Patent Application Laid-Open No. 57-5109 (corresponding to U.S. Pat. No. 4,491,906), and "Introduction to NC Programming", published by Nikkan Kogyo Shimbunsha, Oct. 30, 1981, pp. 156-162. This method is useful in generating a smooth curved surface from section data.
Depending upon machining, there are cases where it is required to machine a complex curved surface obtained by combining two or more three-dimensional curved surfaces, or in other words, to create a complex curved surface. However, it is not possible with the prior art to create a complex curved surface in simple manner by combining these three-dimensional curved surfaces using the data indicative of each three-dimensional curved surface. Accordingly, the applicant has proposed in Japanese Patent Application No. 60-39445 a novel method of creating complex curved surfaces includes inputting data for specifying each three-dimensional curved surface constituting a complex curved surface, inputting data specifying one line of intersection on a predetermined plane (e.g. the X-Y plane) as well as a rule for specifying a number of lines of intersection on the X-Y plane on the basis of said line of intersection, finding a section curve of the complex surface based on a section which has an i-th line of intersection, among the number of lines of intersection, as its line of intersection with the X-Y plane, thereafter obtaining, in a similar manner, section curves based on sections corresponding to respective ones of the lines of intersection, and generating a complex curved surface by assembling the section curves.
There are cases where it is desired to provide a fillet surface (i.e. a rounded surface) of a radius R at the boundaries of the three-dimensional curved surfaces constituting the complex curved surface.
Conventionally, however, these boundaries cannot be provided with roundness of radius R accurately through a simple method. It should be noted that the applicant has proposed a method of providing roundness in International Application No. PCT/JP86/00310.